Purification of esters of orthophosphoric acid



Patented Oct. 30, 1951 UNITEDtsTATs PATENT orti y lWilliam E'. weesn'er, Webster Graves, wgiirgnorio Monsanto Chei'iiiclaljoliipany, St. Louis, vMo.; a corporation Nof Delaware y' Nt Drawing. Applicata@ April 21, 1949,

' ,Serial No. 88,893

"invention relates `t0'IeSter-S'foi 'orthoephbsphiie acid; fmre Yspeeiiically this Vinvention ree l'ts to an improvement in lthe 'process for 'the uiiication of 'esters of ortho-phosphoric acid Having' the formula iii-s l--a t wherein R1, R2 and R; are selected "froi'r'i the rop consisting of allylr'adials haviiigatleast 6 and not more than 18' carbon atn'is and all'ioiq-V ethyl radicals wherein the alkyl substituent contains at least 4 a'i'i'd Inot v'more than 18 carbon atoms.

In the preparation of the above described trialkyl phosphates or trialkoxyethyl phosphates, the formation of fnie'ne or Jdi-'substituted acid phosphates, hereinafter v-referiecl to as partial esters of phosphoric acid, are unavidable, vyet their presence in the finished product -i's-undesirable. These partial esters are insoluble water and at ordinary temperatures', Vthe alkali metal salts of thesepartial esters ofphospleric acid are ii'ioie soluble in the lester lthan in Water which inalies them exceedingly diicult to remove by Washing; Furthermore,- thse patri'al vesters of phosphoric acid which are formed. during the prepara-tion of the ftrialkyl phosphates or t`rialk'oiiyethyl phosphates lwhich are ith subiect ef this invention, are diiiicult to separate from the crude ester by fractionation, as at the temperatures required for such a fractionation, these partial esters tend to decompose releasing Volatile products which further contaminate the finished ester andrender it exceedingly Ydiilicult to maintain the low pressure necessary iorsuch -a 'trace tionation;

Itis an object of this invention :to provide ari improved process vfor thelpurication of -este`r`s 'ci rtho-phosphoric acid. vIt isa furtherobject-f this invention to `provide an improveilV process f-fr the removal-of the partiarestes: er pn-esplicite acid formed during the preparationj'of "trialkyl and trialkoxyethyl phosphates.` Further ,objects vwill become apparent yfrom the description i the novel imprved process of this invention and the elaims.

l It has vnow been `discce''ed :that the iiionor di-substituted esters of phosphoric acid, the scalled partial esters o fphosphoric.acidafoundras ,impurities in .trialkyl ,phosphates or trialk'oxy- -ethylf phosphates, canl easily :be removed from the t'rialky'i pnsphateer -triaikoxyethyi pir-egg plate "by iirst A'convertini;A the partial ester "of phosphoric' aidfto its alkali netal salt, "and then Washing with livai'ie at a teii'iperatr'e eic'ess of 'about 183 C. At higher tempera? ture 'tli'fallali 'irietal salts o'f the partial esters of phosphoric 'cid areinore soluble :Water than the ester, and he'ri'c may be 'Washed iit With= out v`diiiciilty. A l

Iii carrying out the nov'el lpuriiication process of this invention, 'a sui'cie'nt 'quantity o'f alkaline alkali metal salt, that isaii alkali inetal salt -tvhosfe :aqueous solution is v basic vt'o litmus; foi'. an alkali .metal .hydroxide .is added to ythe *crude ester to renderti-1e ester alkaline. Thealkaline alkali metal salt or the alkali metal hydroxide may be added per se or in solution. Typical of ceinpodnds are the phosphates, lbica'rboiiaises,-carbcnatesandhydroxidescisodiurmpotas sima an'dhthium. 4einer the ration-massiis been rendered alkaline, -it is then Ktiifoug'tilg'v Washed with Water ata Ater'nperatur'e -inezclesspf about G., whereupon the :alkali tmetal salts of lthe partial esters vof phosphoric acid laire 'Sife-1 hoved from lthe 'rea'ctioi'rmass fiiieito their-*greater solubility in Water than in the ester at ith-istein: perature. The washing procedure may be carried out any 'of several 'convenient rh The reacticn'mass 'niay'be agitated with ivatr at a tei'riperaturem excess of85'C., and while main'` taining this temperaturathe water layer separated and decanted from the reaction mass. The ',as'hingfg bperatibnniay 'also beijtenieritly earr'red Amit 4by v.intrdting -steaih into 'the yailjfiie reaction mass, aue'wiiie the steam te Vconsense and cool at fa temperature inen'ess fra'biitrSB C., 'andu'a'ftr suieintcodensatio'n ha taken piace, decantiiig :the water paving dissivd therein'thejallali intal'salts f the partial esters 'frphosphoric acid. n i

"lB/pi'cal,'loutv not ei'zhaus'tive, 'of the phosphates that maybe pried ih-theaboveaescnbed ner are those symmetrie@ @riale/,1591* ...trialvkQx-y: ethyl phosphates wherein thesubsitets are straightor branchelhegryl, heptyl,goctyl, nnyl; decyl, dodecyl, tridecyl, tetradecyl, octadeyl, butoxyethyl, hexoiiyethyl, :octoxyethyL decoxyethyl, i .tetradecoxyethyl c vand octadecoxyethyl ibeen found to .beof some utility inthe purifica- Example I 273.0 g. of 2-ethylhexyl alcohol was placed inV a glass reactor and 40 g. of POCls added with stirring at 6 to 10 C. over a period of one hour.

The mass was stirred and heated to 23 C. for a two hour period, after which time vacuum was applied and the heating continued until 80 C.;

and 22 mm. Hg of pressure'was'obtained. The '1'5 mass was held at this temperature and pressure for hours.

50 ml. of water was :then added.

under vacuum. Tri(ndecyl) phosphate was thus obtained in an 86% yield based on POCls and exhibited the following properties:

Acidity as H3PO4 per cent 0.04 Sp. gr. 25/25 C 0.901 N152? i, y f 1.4452

. Crude tri(6methylheptyl) phosphate was prepared in the manner described in Example I utilizing 767g.v of POCla and 520 g. of 6-methyl- 41he`1.`tanol. The partial esters formed in the and the mixture was made alkaline with 2.2 g. of

sodium carbonate. Excess alcohol was then removed by heating the mass gradually to 142 C.-

under mm. Hg pressure. Water was then add- .edV to the material left' in the reactor, and the mass Was steamed at 100 to 105 C. until 300 ml. of distillate had been collected. The Water layer was still alkaline after steaming and the mass was settled at 90 to 95 C. and the water layer drained oi. VFive additional water washes was lmade at 90 to 95 C. to complete the removal of partial esters. The ester layer was then dried under vacuum at about 100 C. The tri(2ethyl hexyl) phosphate thus obtained had the following physical properties:

Acidity as HaPO4 per cent-- 0.015

Sp. gr. 25/25 C 0.9195

Color Nearly water white Example II Acidity as H3PO4 per cent-- 0.002 Sp. gr. 25/25 C 0.937 Nn 1.4340

Example III Y Crude tri(noctyl) phosphate was prepared as described in Example I utilizing 1,188.2 g. of n-octyl alcohol and 230.3 g. of POCls. The n-octyl acid phosphates in the crude ester were removed by iirst forming their alkali metal salts by adding sufficient sodium carbonate to render the entire reaction medium alkaline, and then washing with Water at aboutV 100 C. The washed ester was then dried under vacuum and the thus refined material had the following properties:V

Acidity as H3PO4 per cent 0.02

Sp. gr. 25/25 C 0.915

Example IV The crude tri(n-decyl) phosphate was prepared in the manner described in Example I utilizing 533.0 g. of n-decanol and 84.4 g. of POCla. The partial esters formed in the preparation were removed by treating the reaction mass until alkaline with an alkaline alkali metal salt, sodium carbonate, and then washing with water at about 95 C. The washed ester was then dried preparation Ywere removed by treating the reaction'mass until'alkaline with potassium carbonate, 4and Vthen washing with water at about 100 C. lThe vwashed ester was dried under 'vacuum thereby obtaining in excellent yield and purity tri(6methylheptyl) phosphate.

v y Example VI Crude tri(betabutoxyethyl) phosphate, was prepared lin themanner described in vExample I using 944 g. of ethylene glycol monobutyl ether and 154.4 g. of POCls. The partial esters were removed by rendering the cruderester alkaline by the addition of sodium hydroxide followed by washing with water at a temperature in the range oi about to 90' C.A Thewashed ester was dried under vacuum thereby obtaining substantially pure tri(betabutoxyethyl) phosphate.

What is claimed is:

1. In the process for the purication of esters of ortho-phosphoric acid having the formula wherein RyRz and R3 represent a radical selected from the group consisting o f alkylradicals having atleast 6 and not more than 1S carbon atomsand alkoxyethyl radicals wherein the alkyl substituent contains at leastfl vand not more than 13 carbon atoms, the ,Steps comprising adding .to the crude ester a compound selected from the group consisting of the alkaline alkali metal salts and alkali metal hydroxides so as to render saidl crude ester alkaline and then washing with water at a temperature in excess of about 85 C. N

2. In the process for the purification of ,esters of ortho-phosphoric acid having the formula wherein R1, Rg and R3 represent anV alkyl `radical having at least 6 and not more than'18 y carbon atoms, the steps comprising adding to theV crude ester a compound selected from the group consisting of the alkaline alkali metal salts and alkali metal hydroxides so as to render said crude ester alkaline and then washing with water at a temperature in excess of about85 C.

3. In the processY for the purification of a trioctyl phosphate'the steps comprising adding to the crude trioctyl phosphate a' compound selected from the "group consisting of the al'- kaline alkali metal salts and alkalil metal hy"- droxides so as to render said lcrude trioctyl phosphate alkaline and then. washing with water at a temperature in excess of about 85 C. 1 j

4. In the process yforthe Apurification of tri'- (2-ethylhexyl) phosphate vthe steps. comprising adding to the crude tri(2ethylhexyl) phosphate a compound selected from the group consisting of the alkaline alkali metal salts and alkali metal hydroxides so as to render said crude tri(2ethyl hexyl) phosphate alkaline and then Washing with Water at a temperature in excess of about 85 C.

5. In the process for the purication of tri- (G-methylheptyl) phosphate the steps comprising addingA to the crude tri(6methylheptyl) phosphate a compound selected from the group consisting of the alkaline alkali metal salts and alkali metal hydroxides so as to render said crude tri (-methylheptyl) phosphate alkaline and then washing with Water at a temperature in excess of about 85 C.

6. In the process for the purification of esters of ortho-phosphoric acid having the formula wherein R1, R2 and R3 represent an alkoxyethyl radical wherein the alkyl substituent contains at least 4 and not more than 18 carbon atoms, the steps comprising adding to the crude ester a compound selected from the group consisting of the alkaline alkali metal salts and alkali metal hydroxides so as to render said crude ester alkaline and then washing with Water at a temperature in excess of about C.

7. In the process for the purication of tri- (beta-butoxyethyl) phosphate the steps comprising adding to the crude tr(betabutoxy ethyl) phosphate a compound selected from the group consisting of the alkaline alkali metal salts and alkali metal hydroxides so as to render said crude tri(beta-butoxyethyl) phosphate alkaline and then washing with water at a temperature in excess of about 85 C.

WILLIAM E. WEESNER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,844,408 Nicolai Feb. 9, 1932 1,869,768 Nicolai Aug. 2, 1932 1,931,059 Clemmensen Oct. 17, 1933 2,157,164 Daly May 9, 1939 FOREIGN PATENTS Number Country Date 328,963 Great Britain Apr. 30, 1930 Certificate of Correction Patent No. 2,573,658 October 30, 1951 WILLIAM W. WEESN ER It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 4, line 24, for and 154.4 read and 153.4;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oice.

Signed and sealed this 19th day of February, A. D. 1952.

THOMAS F. MURPHY,

Assistant Uommz'ssonef of Patents. 

1. IN THE PROCESS FOR THE PURIFICATION OF ESTERS OF ORTHO-PHOSPHORIC ACID HAVING THEFORMULA 